Abstract
Mechanisms of aging phenotypes such as the decline in muscle mass and strength are unknown. In the Baltimore Longitudinal Study of Aging (BLSA), adiposity was the strongest correlate of low muscle quality both cross-sectionally and longitudinally. Fat in muscle may cause problems to: 1) mitochondria oxidative phosphorylation; 2) energetic metabolism; 3) muscle fibers structural integrity. Mitochondrial muscle bioenergetics assessed by phosphorus MRS was associated with walking performance and such association was mediated by impaired strength. Participants with impaired mitochondria energetics had experienced larger weight gain over previous 20 years. Low muscle quality was associated with higher levels of circulating leucine, isoleucine, tryptophan, serotonin, and methionine. In MRI and EM analysis, the architecture of muscle fibers were distorted with fractures in the continuity of serial sarcomeres in older individuals. Increasing adiposity may lead to impaired mitochondrial function, reduced protein homeostasis, with negative consequence on muscle structure and function.
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